The mortality experience of workers at a copper smelter at Tacoma, Washington producing nearly all the arsenic trioxide produced in the United States will be studied. Men employed a year or more since January 1, 1940 will be followed for deaths through December 31, 1975. The cancer mortality experience of this cohort will be related to duration and intensity of arsenic exposure and latent period. Both historic atmospheric measures of arsenic and urine arsenic testing of workers will be used to estimate exposures. In addition, the mortality experience of persons living near the smelter will be studied to see if any effect of atmospheric contamination on cancer mortality can be detected. This will include follow-up on children from an elementary school in the area using school records dating to 1910. Also included is a study of mortality in the area adjacent to the smelter and where elevations in urine arsenic have been found apparently related to the smelter.